Color tube having venetian blind-type color selection grid and integrally formed baffles on display screen



315 449 OR 395469517 5R w. VEITH 3,546,517

SNETIAN BLIND-TYPE COLOR SELECTION GRID 4 FORMED BAFFLES ON DISPLAYSCREEN Filed June 6, 1968 Fig.1 1

Patented cc. 8, 197% US. Cl. 313-69 5 Claims ABSCT OF THE DISCLOSURE Asingle gun plural cathode ray tube having a plurali ty of grids atvarying potentials in which an electrostatic focusing lens is providedfor focusing on an electron receiving screen all of the beams passedthereto from the cathodes and associated grids, and the plural beams aremade to cross each other at the optical center of the lens forminimizing aberrations of the beam thereby, a grid is provided betweenthe electrostatic focusing lens and the associated grids which is atground potential to eliminate the deleterious effects of intergridinterference. The provided grid also has enlarged electron beamreceiving apertures therein in relation to the associated grids whichare adjacent thereto to facilitate the placement of the apertures in theprovided grid in the path of the electron beam thereby obviating theneed for close tolerances.

This invention relates generally to improvements in cathode ray tubes ofthe type, as particularly disclosed in US. Pat. No. 3,448,316 whichissued on June 3, 1969, in which a single electron gun is provided foremitting a plurality of electron beams to produce a color picture, forexample, as in color television receivers. It should be understood,however, that the teachings of this invention are applicable to pluralguns for color and to black and white receivers also.

This application is a continuation-in-part application of co-pendingpatent application Ser. No. 697,414, filed June 12, 1968, and entitled,Cathode Ray Tube which issued on June 3, 1969 as US. Pat. No. 3,448,316.

In the development of electron guns for cathode ray tubes especially inthe field of color television, there are two basic systems. In theconventional system three independent electron gunsare utilized whichemit electron beams. These beams are modulated by corresponding colorsignals and acted upon by a grid system so as to be focused on acollector or electron receiving screen which may be simply a phosphor orluminescent screen with a perforated electrode or shadow mask locatedadjacent thereto. It has been found that .using three independentelectron guns to produce the beams is costly and by reason of the spacerequired for the three guns, the available flexibility for miniaturizingthe tube is limited.

To avoid the latter disadvantages, it has been proposed to provide acolor picture tube of the single-gun, plural beam type in which a singleelectron gun emits three beams from either three respective cathodes ora single cathode. The plural beams can then be passed through alens-like focusing system, so as to converge at the electron receivingscreen. r

In both systems the cathodes are each housed within a grid having anaperture therein and this grid is at a potential with respect to thecathode. One or more addi tional grids, having apertures therein for thereception of electrons, and also having a desired potential appliedthereto are used to accelerate the beam and properly converge it on theelectron receiving screen. The grids are spaced from each other axiallyand radially in a cathode ray tube generally in the neck portion of thetube. The electric fields emitted by the bias placed on the grids canaffect another grid which is within its field if'it is not spaced farenough from the field. Unfortunately, the amount of space available inthe neck of a cathode ray tube does not permit a wide latitude inspacing, and the strength of the field is important as it relates to thegrid from which the electron beams are to be properly at tracted.Therefore, when two or more grids must be necessarily close together forproper operation, the deleterious etfects of intergrid interference arepresent, and a distorted picture on the electron beam receiving screencan result.

To eliminate these deleterious effects, it has been found that bymaintaining an intermediate grid at ground potential, it functions as ashield which protects one grid from stray electric fields caused byadjacent grids.

It is -also known that prior art grids use an aperture therein for thereception of the electron beams. The apertures are very small and mustbe carefully aligned with the beam emitted from a cathode or the beamwill deflect from the grid and a distorted picture will appear on thescreen, if indeed it appears at all. As a result of this, elaborate jigsand fixtures had to be devised to insure the precise placement of thegrids. Even with the latter expensive jigs and fixtures, an inordinateamount of assembly time: had to be spent in grid alignment because theplacement is so critical.

To overcome this disadvantage, applicants devised an improved gridsystem which does not utilize the uniform size aperture commonlyemployed in the prior art. It has been found that by making the size ofthe openings of one grid larger with respect to the other that thecritical placement of one grid with respect to the other has beeneliminated. This is true because a larger area is available throughwhich the beam can pass and a slight misplacement or movement of a gridwill not distort the emitted beam because it can still pass through thelarger grid opening.

In the following detailed description of an illustrative embodiment,particular reference is made to a single-gun, plural-beamsystem which isused in color picture tubes, but it is to be understood that thedescribed single-gun, plural-beam system according to this invention canbe applied to any other gun used in a plural beam cathode ray tube. orin any electronic devices using a grid or elec trode system toaccelerate an electron beam.

The above features and advantages of this. invention will becomeapparent from the following detailed description of an illustrativeembodiment which is to be read in conjunction with the accompanyingdrawings, in which: .1

The; figure is a schematic longitudinal sectional view showing aplurality of cathodes and grids in an: improved plural beam electrongun.

Referring to the figure there is shown a plurality of cathodes 10, 11and 12, having respective electron-emit ting surfaces, which arearcuately arranged in a horizontal plane the surfaces being arranged sothat perpendiculars thereto converge and extend through the opticalcenter F of the lens. The cathodes are so arranged so as to eliminatethe necessity of an auxiliary lens to converge the emitted beams whichis more fully discussed in co-pending application Ser. No. 697,414,filed Jan. 12, 1968, and entitled Cathode Ray Tube, which issued on June13, 1969 as US. Pat. No. 3,448,316. Each cathode has a respective grid13, 14 and 15 having a potential applied thereto, which can surround thecathode and has an aperiure 16 located approximately in the center ofthe face in? the grid enabling it to function as a window for an emittedheam B B 1 and B from the respective cathndes. The apertured faces orend walls of the grid 13, 14 and 15 are parallel to and equidistantlyadjacent to the respective electron-emitting surfaces of the respectivecathodes 1t 11 and 12.

A grid 17 having an arcuate face 18 thereon has a plurality of apertures21 therein each of which receives a respective electron beam. Anelectrical potential of suitable value is impressed on the grid 17thereby causing the emitted electrons to converge substantially at anoptical center F of a focusing lens L. Additional grids 19 and can beused to produce the desired effects on the emitted electron beams. Thegrids can be in the form of an enclosure which is open at one endthereof or open at both ends. These grids 17, 19 and 20 comprise anelectrostatic focusing lens, and, as disclosed in my previously referredto copending application, now US. Pat. No. 3,448,316, grids 17 and 20may be at a high potential 1 while grid 19 may be at a low potential.

The aforementioned cathodes and grids are located in the neck of acathode ray tube which is a relatively small miniature televisioncabinet. In order to reduce the length of the neck of the tube, it isnecessary that the grids 13, 1d, 15 and 17 be brought into closeproximity. The electric field which radiates from the grid 17 canthereby affect each grid 13, 14 and 15 in a different manner because ofthe arcuate arrangement of the grids. For example, the distance from theface of the grid 13 to the point where the emitted beam enters theaperture 21 on the face of the grid 17 is greater than the distancebetween the face of the grid 14 to the corresponding aperture 21 on grid17. Since the strength of the electric field at a particular point is afunction of distance, the effect on an electron at the face of grid 13and at the face of grid 14- will be different. The emitted beams will,therefore, be distorted and an undesirable picture can result. Toovercome this problem a grid 22, which may be cup-shaped as shown in thefigure, is mounted between the grids 13, 1 5, 15 and 17 preferably closeto the cathodes. This grid 22 may have an end wall, portions of whichare equidistant from and substantially parallel to the aperttlred facesof the grids 13, 14 and 15, and these end'wall p ortions may be surfacesof revolution such as may be present when the end wall is an arcuatesurface concentric with the arcuate surface to which the apertured facesof the grids 1.3, 14 and 15 are tangent. The grid 22 has a plurality ofapertures 23 therein which are aligned with the respective apertures 16in the grids 13, 14 and 15 and which may be larger than these apertures16. It has been found that if the apertures 23 are approximately twicethe size of the apertures 16 that the beneficial results of theinvention can be achieved. This will be more fully discussed below.

The grid 22 is at ground potential whereby it functions somewhat as ashield for the grids 13, 141 and 15. The effect of placing the grid 22adjacent the cathode grids 13, 14 and 15 is to effectively apply thesame strength electric field to the cathode grids despite their varyingdistances from the grid 17.

As pointed out above the apertures 23 in the grid 22, which is at groundpotential, are approximately two or more times the size of the apertures16 in the cathode grids 13, 14 and 15. It is obvious that the electronbeams E B and B emanating from the respective cathodes 1%, 11 and 12must enter the apertures 23 in the face of the grid 22. Since the sizeof the openings in the grid 22 are much larger than the openings 16 inthe cathode grids 1d, 11 and 12, the criticality of locating theopenings in the grid 22 in line with the beams from the cath- 4 odes 10,11 and 12 is greatly diminished. If the grid 22 is not perfectly placedin relation to the cathode grids 1t), 11 and 12 the beams B B and B willstill pass through the openings 23 in the grid 22 because they now havea larger area into which they can pass.

While they has been shown and described a single embodiment of theinvention, it will be obvious to those skilled in the art that changesand modifications may be made Without departing from the invention, andthat it is intended by the appended claims to cover all such changes andmodifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. A single-gun, plural-beam cathode ray tube comprising anelectron-receiving screen, a plurality of spaced cathodes for generatingrespective beams and having electron emitting surfaces arranged so thatperpendiculars thereto converge and cross each other at a point in saidtube intermediate said cathodes and said screen with said electronemitting surfaces being substantially equidistant from said point,electrostatic focusing lens means com mon to all of said beams to focusthe latter on said screen, said lens means having an optical center andbeing located to dispose said optical center substantially at saidpoint, first control grids respectively associated with said cathodesand including end walls parallel and equidistantly adjacent to saidelectron emitting surfaces of the respective cathodes, said end Walls ofthe first control grids having apertures for the passage therethrough ofthe respective beams, and a common second grid interposed between andspaced from said first control grids and said electrostatic focusinglens means, said second grid being cup-shaped and including an end wall,portions of which are equidistant from, and substantially parallel tosaid end walls of the first control grids, said portions of the end wallof said second grid having apertures therein substantially aligned withrespective apertures of said first control grids, said electrostaticfocusing lens means including a grid to which a high potential isapplied and which is disposed adjacent said second grid in axiallyspaced relation thereto, and said second grid being grounded to preventelectrical discharges between said high potential grid of the lens meansand said first con trol grids.

2. A cathode ray tube according to claim 1, in which said apertures ofthe second grid are substantially larger than said apertures of thefirst control grid to ensure free passage of said beams through saidapertures of the sec- 0nd grid even when the apertures of said first andsecond grids are imprecisely aligned.

3.. A cathode ray tube according to claim 2, in which said apertures ofthe second grid are at least twice as large as the respective aperturesin said first grids.

4. A cathode ray tube according to claim 1, in which said end wallportions of the second grid are parts of a surface of revolution.

5. A cathode ray tube according to claim 1, in which said end wallportions of the second grid are parts of an arcuate surface having itscenter of curvature at said point, and said end walls of the firstcontrol grids are tangent to an arc concentric with said arcuate surfaceof the second grid.

References Cited UNITED STATES PATENTS 2,887,598 5/1959 Benway 313-70JAMES W. LAWRENCE, Primary Examiner V. LAPIRANCHI, Assistant ExaminerUS. Cl. XJR. 315-13

